1. Field of the Invention
This invention relates to adhesive silicone compositions providing cured products having improved adhesion to various organic resins and improved release from molds.
2. Prior Art
A number of methods have been proposed for providing a bond between addition curing type silicone rubber and organic resins. It is known, for example, to form a bond by applying a primer to a surface of molded resin, applying uncured silicone rubber material thereto and curing the silicone rubber to the resin. Another typical method is by curing self-adhesive silicone rubber compositions directly to molded resin. For the self-adhesive silicone rubber compositions, a number of proposals have been made on their tackifier component.
As another approach, it is known from U.S. Pat. Nos. 4,582,762, 4,686,124, 4,814,231 and 4,834,721 corresponding to Japanese Patent Publication (JP-B) No. 34311/1990 to add an organohydrogenpolysiloxane containing at least 30 mol % of hydrogen atoms directly attached to silicon atoms to an organic resin (e.g., olefin resin) so that the resin is bondable with addition curing type silicone rubber. JP-B 45292/1988 discloses integration by physically fitting silicone rubber within molded organic resin. In EP 276,790A and CA 1304206 corresponding to Japanese Patent Application Kokai (JP-A) No. 183843/1988, a compound having an aliphatic unsaturated group and a hydrolyzable group attached to a silicon atom is grafted to an olefin resin and silicone rubber is bonded and integrated with the grafted olefin resin.
However, several problems arise with these prior art methods for integrating silicone rubber and organic resin into a one-piece article. The primer method is cumbersome in that a once molded resin shape must be taken out of the mold before the primer can be applied thereto. The method of applying and curing a self-adhesive silicone rubber composition to molded resin has the serious problem that if the resin and silicone rubber are molded into a one-piece member using a mold, the silicone rubber itself sticks to the mold.
Where organohydrogenpolysiloxane is added to an organic resin, typically olefin resin, the properties of the resin itself can be altered thereby, preventing the resin from exerting its own properties. The physical engagement method leaves a possibility that the two segments be disengaged by physical forces. The use of an olefin resin having grafted thereto a compound having an aliphatic unsaturated group and a hydrolyzable group attached to a silicon atom cannot dispense with a primer when it should be joined to addition curing type silicone rubber. This is cumbersome and uneconomical.
To take advantage of the weatherability, heat resistance, cleanness and rubbery elasticity of silicone rubber, the demand that organic resin and silicone rubber be integrally molded into a one-piece article under curing conditions within a short time is increasing. Under the circumstances, addition curing type silicone rubber is believed best from the standpoints of brief curing and sealing properties. None of the prior art methods are successful in forming an effective bond between addition curing type silicone rubber and organic resin.
Therefore, an object of the present invention is to provide an adhesive silicone composition offering a cured product which is capable of forming an effective bond to organic resins, but smoothly releasable from molds.